Self-association of insulin will be examined as a function of temperature and solvent conditions (pH, ionic strength, concentration of Zn ions and other solvent components) so as to determine stoichiometries, equilibrium constants and other thermodynamic parameters of the insulin-insulin interactions. These data will be used in attempts to delineate the molecular basis of the interactions between insulin molecules. The main component of bovine insulin will be studied most intensively, but studies are also planned on some of the des-amido bovine insulins, on porcine insulin, and, if circumstances permit, on other selected insulin molecules and on appropriate insulin derivatives. Particular care will be taken to isolate and use purified insulin components, as homogeneous as feasible. The primary observation technique to be used will be equilibrium ultracentrifugation. Procedures and instrumentation to increase experimental precision will be designed and implemented. Much effort will be spent in tests of the thermodynamic reversibility of the associations so as to detect the possible existence of metastable conformational forms of insulin. Attempts will be made to isolate and characterize such metastable conformers if they are found to be present.